Conventionally, a plurality of methods of producing industrial multi-layered fabric are widely known. For example, in a so-called span-bond method, requirements such as a lateral rigidity, a diagonal rigidity, and a sheet supportability are needed in the industrial multi-layered fabric. Since the industrial fabric is laterally moved during its running, for a machine for producing the industrial fabric, a palm needs to be applied to the industrial fabric to restrict its movement. Such being the case, in a case where the lateral rigidity of the industrial fabric used is low, a technical problem that the industrial fabric is folded due to the interference by the palm can rise.
In addition, permeability required for the industrial fabric needs to be appropriately set, in accordance with the fabric to be woven. If the permeability is too high, the fiber can be removed off, while if it is too low,
More specifically, a fabric shown in FIG. 19 in Patent Publication 1 was adopted as a conventional fabric. Although such conventional fabric exhibits an excellent permeability at the beginning of its use, a technical problem that the fibers gets stuck into the fabric with time due to its repeated use for producing non-woven fabric has arisen. Here, a sticking phenomenon is defined to a phenomenon in which the fibers are caused to enter into between intersections of knuckles of wires. If the sticking of the fibers are caused, technical problems that the wires mates with the non-woven fibers, or that the permeability of the fabric is increased can rise.
In addition, generally, the knuckle connected to a single yarn tends to have a strong intersection supporting force, while, the knuckle connected to a plurality of yarns tends to have a weak intersection supporting force. For this reason, a structure in which the intersection supporting force is the strongest is a plain weaving structure. In the plain weaving structure, since each of all the knuckles constitutes the one connected to a single yarn, the knuckle density is the highest.
However, in the general industrial fabric, since the surface density gets decreased if the diameter of the wefts is enlarged, so that the lateral density and the surface density are not convertible. That is why it is technically difficult to produce the plain weaving structure.
In order to solve such technical problem, the non-woven multi-layered fabric which exhibits the good permeability, the good lateral rigidity, good sticking of the fiber, the good surface density, the good diagonal rigidity, and the good sheet supportability was devised (Patent Publication 2).
On the other hand, the fabric is formed by weaving wefts and warps with each other. A shape of each of the woven yarns is caused to vary due to the fact that it is folded or bent in every direction. In addition, since a tension force is applied to the warp when the fabric is thermally processed, the woven yarns tend to largely deform in the weft direction. In other words, it is well known that the fabric can curl in its widthwise direction.
Further, various kinds of yarns constituting the fabric are known. For instance, the material of the yarn can be selected freely and usable examples of it include polyester, polyamide, polyphenylene sulfide, polyvinylidene fluoride, polypropylene, aramid, polyether ketone, polyethylene naphthalate, and polytetrafluoroethylene. However, in a case where such above yarns are adopted for the fabric, the fabric tends to curl in its widthwise direction due to the fact that the yarns can shrink upon the thermal process of the fabric. In addition, in the two-layered fabric, the diameter of the upper surface side fabric can be different from that of the lower surface side of the fabric, or the number of the upper surface side fabric can be different from that of the lower surface side of the fabric.
Under such circumstances, the fabric can readily curl in its widthwise direction due to the fact that the shrinking force of the upper surface side fabric differs from that of the lower surface side fabric.
Such a technical problem of the curling of the fabric can rise in the non-woven multi-layered fabric disclosed in the Patent Publication, and an effective means for solving such a technical problem has not been found so far.
Patent Publication 1: Japanese Patent No. 2558154
Patent Publication 2: WO/2012/140992